I had similar probs with my lo. I would put her in the crib, and she wouldn't cry, but would look around forever. After observing her for a few nap times i decided that i needed to block out stimulation to teach her not to look around, as suggested in the books.
here's what i did: I placed my hand over her eyes, resting the top of my hand on her forehead gently. If she was very mad and thrashing her head back and forth at this i would just stroker her head. and slowly i would keep my hand over her eyes a little longer every stroke, until she was comfortable with my hand being there. THIS DIDN"T BECOME A PROP, for whatever reason. She falls asleep on her own now without needing any help, although it did take time (i am talking about 2 months to get her on a perfect routine, and every now and then there are bumps. It seems that things smooth out around 4-5 months, although there are bumps at that time too) Another alternative is to have a very darkened room where there isn't really any stimulation for them. Just a few thoughts!
My lo would also be in the crib a long time (45 minutes) with me covering her eyes and rubbing her tummy, while she was very awake and kicking her legs around (sign that she is tired/overtired). eventually she would cry/fuss, and then fall asleep maybe 20 minutes after that.
Keep up the good problem solving and things will come around if you stick with teaching your baby new sleep associations!
-j